This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Polyketide synthase, a multi-domain enzyme complex, makes many anticancer and antibiotic natural products in a combinatorial fashion by domain shuffling. Polyketide synthase is capable of generating huge variety of ?unnatural? natural products via a controlled variation of chain length and regio-specific formation of rings. Crystal structures of the polyketide synthase components are crucial for such maneuver. Aromatase (ARO) is the key component that controls the formation of aromatic ring of many anti-cancer and antibiotic polyketides, such as daunorubicin, griseusin and tetracycline in a highly specific manner (C7-C12 or C9-C14), however no crystal structure is available for ARO. ARO structure will enable mutations to alter the regiospecificity of ring formation (e.g. C11-C16). Native ARO crystals diffracted to 2.0 [unreadable]. KBr, NaI and selenomethionine-derivatized ARO crystals were also grown. In addition, we obtained crystals of the chain elongation domain (ZhuH) and extender unit domain (FkbI and FkbG). Beamtime at SSRL will be vital for us to solve the crystal structure ARO, ZhuH, FkbI and FkbG using MR, MAD or MIR methods. These polyketide synthase domain structures will be utilized in a combinatorial fashion to generate novel anticancer and antibiotic drug leads.